Table 1 Search strategy for extraction of relevant studies

MEDLINE

1. exp acute pain/

2. exp. low back pain/

3. exp. analgesics, opioid/

4. exp. morphine/

5. exp. codeine/

6. exp. fentanyl/

7. exp. tramadol/

8. exp. meptazinol/

9. exp. pentazocine/

10. exp. methadone

11. exp. buprenorphine/

12. oxycodone.mp.

13. dipipanone.mp.

14. remifentanil.mp.

15. papaveretum.mp.

16. pethidine.mp.

17. tapentadol.mp.

18. 1 or 2

19. 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 or 15 or 16 or 17

20. 18 and 19

21. Limit 20 to humans

EMBASE

PsychINFO

CINAHL

Web of Science

Cochrane Library

Cochrane Clinical Trials Registry

National Institutes for Health Clinical Trials Registry

World Health Organization International Clinical Trials Registry Platform